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Abstract

Oxygen consumption varies with physical and mental activity as well as pathological conditions. Although there is a strong relationship between yoga and metabolic parameters, the relationship between yoga and oxygen consumption has not yet been formally reviewed. This systematic review attempted to include all studies of yoga that also measured oxygen consumption or metabolic rate as an outcome. A total of 58 studies were located involving between 1 and 104 subjects (average 21). The studies were generally of poor methodological quality and demonstrated great heterogeneity with different experimental designs, yoga practices, time periods, and small sample sizes. Studies report yoga practices to have profound metabolic effects producing both increase and decrease in oxygen consumption, ranging from 383% increase with cobra pose to 40% decrease with meditation. Compared to nonpractitioners, basal oxygen consumption is reported to be up to 15% less in regular yoga practitioners, and regular yoga practice is reported to have a training effect with oxygen consumption during submaximal exercise decreasing by 36% after 3 months. Yoga breathing practices emphasize breathing patterns and retention ratios as well as unilateral nostril breathing, and these factors appear critical in influencing oxygen consumption. A number of studies report extraordinary volitional control over metabolism in advanced yoga practitioners who appear to be able to survive extended periods in airtight pits and to exceed the limits of normal human endurance. More rigorous research with standardized practices is required to determine the mechanisms of yoga’s metabolic effects and the relevance of yoga practices in different clinical populations.

Keywords

yogic meditation metabolic rate/cost oxygen consumption energy expenditure

Introduction

Human metabolism is the result of continuous anabolic and catabolic processes that maintain homeostasis and sustain life. Metabolic pathways include a complex network of nutritional, neuronal, and humoral inputs that are integrated by the central and autonomic nervous systems through pathways that monitor and maintain physiological functioning. All metabolic processes generate heat and are ultimately dependent on the expenditure of energy via consumption of oxygen, which drives oxidative phosphorylation.

Energy expenditure is a directly related to metabolic rate and oxygen consumption, and these terms are often used interchangeably. Monitoring oxygen consumption has received a great deal of interest in determining oxygen delivery to tissues, cardiorespiratory function, and metabolic response to activity. Assessment of oxygen consumption is used in determining energy requirements for healthy lifestyles, exercise programs, and critically ill patients.^1
–3 Oxygen consumption is reported to increase with adaption to physiological stress and pathology.^4,5 The measurement of energy expenditure can be performed via direct calorimetry, which measures heat loss using insulated chambers, or via indirect calorimetry, which directly measures oxygen consumption⁶ through respiratory gas exchange. Direct calorimetry is not frequently used as it is complex, does not accurately measure rapid changes in metabolism, and requires significant expertise and elaborate equipment including specially constructed chambers. Indirect calorimetry is the most commonly used technique for measuring energy expenditure and can be used to measure the substrate of metabolism as well as oxygen consumption, which can be expressed in terms of VO₂ (absolute oxygen consumption), VO₂/kg/min (relative oxygen consumption), and MET (metabolic equivalent task).^2,3,7

Oxygen Consumption, Stress, and Pathology

Oxygen consumption is maximal during intense physical activity and lowest during basal or resting conditions and higher oxygen consumption is associated with psychological and physiological activity, stress, pathology, and accelerated aging.^4,5,8,9 Oxygen consumption has also been found to increase with activities such as mental arithmetic and playing video games,^10

–13 as well as with psychological distress and anxiety.¹⁴ A growing body of research further suggests that oxygen consumption is higher in various pathological conditions, including congestive heart failure,¹⁵ locomotor impairment,¹⁶ HIV,¹⁷ chronic obstructive pulmonary disease,¹⁸ insomnia,² and congestive heart failure.¹⁹ Oxygen consumption has also been found to increase with features of metabolic syndrome, including obesity,^20
–22 type 2 diabetes,^23

–26 and hypertension.^27
–29

The measurement of oxygen consumption can provide insights into overall homeostatic balance and response to stress, which are mediated through multiple pathways under the control of the autonomic nervous system and the hypothalamus. The sympathetic nervous system is involved in rapidly mobilizing vital physiological functions via sympathetic–adrenal–medullary pathways in response to acute stress,^30
–32 which serves to increase oxygen consumption. Repeated or chronic stressful stimuli may lead to changes in the hypothalamic–adrenal–pituitary axis, leading to a sustained stress response involving cognitive, emotional, endocrine, and immune system changes.³³ The parasympathetic nervous system provides a counter to the stress response and reduces oxygen consumption by activating the so-called relaxation response,³⁴ which serves to reduce physiological arousal and induce a hypometabolic state mediated via enhanced vagal activity.³⁵ Such hypometabolic states are suggested to enhance survival in plants and animals by facilitating restorative and repair functions.³⁶

Yoga, Stress, and Metabolism

Mind–body practices that induce relaxation have been traditionally used by people across cultures to improve health and serve as a path for spiritual awakening.³⁷ Yoga is an ancient mind–body approach that combines the practice of postures (asana), breathing (pranayama), and meditation (dhyana) with the aim of achieving an effortless state of harmony (samadhi).

Yoga postures include both static and dynamic postures that are designed to attune the body to a stable state suitable for meditation. Yoga breathing includes a range of practices such as Bhastrika (bellows breath), Ujjayi (victorious breath), Kapalbhati (lustrous cranium), and unilateral nostril breathing, which can be performed at different rates (reported as breath/minute) and with different retention periods and patterns that involve either internal retention (inspiration–retention–expiration) or external retention (expiration–retention–inspiration). The yogic state of meditation is characterized by decreased oxygen consumption and cardiovascular activity^35,38 and has been shown to elicit the relaxation response.³⁴ This meditative state, which is distinct from rest,^39,40 physical relaxation,⁴¹ and sleep,⁴² may be voluntarily induced, even while performing fixed physiological workloads.⁴³

The ability of yoga to induce relaxation and relieve stress has been widely reported,^44
–46 and there are reports of yoga practices reducing acute, chronic, and posttraumatic stress. For example, yoga is reported to relieve workplace stress,⁴⁷ examination stress,^48,49 and stress-induced inflammation.⁵⁰ Yoga practices have also been reported to improve many clinical conditions such as anxiety,^51
–53 depression,^53,54 negative mood states,^55

–58 and posttraumatic stress disorder (PTSD) symptoms in war veteran,^59
–61 tsunami survivors,^62,63 hurricane refugees,⁶⁴ and flood survivors.⁶⁵ Furthermore, 2 reviews, one involving 35 clinical studies⁶⁶ and the other 8 controlled trials of healthy adults,⁶⁷ acknowledge the promising role of yoga in reducing stress. Li et al also suggest yoga as a potential adjunct to pharmacologic therapy for patients with stress and anxiety.⁶⁶ There are further studies to suggest that regular yoga practice reduces physiological and metabolic activity under normal conditions. Compared to nonpractitioners, regular yoga practitioners have been found to have lowered resting heart rate,⁶⁸ blood pressure,⁶⁸ breath rate,⁶⁹ and metabolic rate.^70,71 Yoga has also been found to improve all features of metabolic syndrome, including obesity,^72,73 hyperlipidaemia,^74
–76 hyperglycemia,^75,77,78 and hypertension,^79
–81 with 3 separate randomized controlled trials demonstrating benefits of yoga in metabolic syndrome patients.^82
–84

While there seems to be a strong relationship between yoga and metabolic parameters, the relationship between yoga and oxygen consumption has not been formally reviewed. The objective of this article is to systematically review previous research exploring the relationship between yoga and oxygen consumption and explore the impact that different yoga practices has on oxygen consumption in different populations.

Methodology

For this systematic review, a comprehensive search of multiple databases including Scopus, PUBMED, PSYCHINFO, CINAHL, Science Direct database was conducted, and a separate search was conducted in Indian medical journals through IndMed, which indexes more than 100 prominent Indian scientific journals. Similarly, a search was performed of Yoga Mimamsa, which includes published yoga research literature dating back from 1920 not listed in the above databases. The archives of the International Journal of Yoga were also searched, along with the reference citations from all full-text articles identified. The primary search terms included Yoga, yogic, pranayama, yoga nidra, breathing, relaxation, meditation, Transcendental meditation, Brahamakumari meditation, Raja Yoga meditation, Om meditation, mantra meditation, Sahaj Yoga meditation, cyclic meditation, and Kundalini yoga, Kriya yoga, and Sudarshan Kriya along with keywords oxygen consumption, energy expenditure, metabolic cost, and metabolic rate.

All studies that had oxygen consumption (at resting, during yoga intervention, or during physical exercise in which yoga included in the intervention) as an outcome were included in the systematic review. The search was performed for articles published up to December 2012 and was not otherwise restricted by date or study population. The review included studies that examined a range of yoga practices including asana and/or integrative yoga, breathing, meditation and yogic relaxation practices used either alone or as an integrated practice. The studies were excluded if they were not in English (n = 4), unobtainable (n = 5), in press (n = 8), or only documented study protocol (n = 5). Studies were also excluded if they only involved meditation (religious or nonreligious) and relaxation practices that are not directly associated with yoga such as Zazen/Zen Buddhist meditation, Vipassana Meditation, Tum-Mo yoga, Qigong, relaxation response, progressive muscle relaxation, and autogenic relaxation. However, it was beyond the scope of this systematic review to collect and synthesize clinical outcomes other than oxygen consumption or critically assess the methodological quality of all studies. The selection of relevant studies is shown in Figure 1, and the results, including their statistical significance, are noted in the relevant text and tables.

Figure 1.

Flow chart of study search and included studies.

Results

A total of 58 studies of oxygen consumption and yoga practices were extracted (Figure 1). These studies involved between 1 and 104 subjects (average 21) and demonstrated great heterogeneity with many different experimental designs, yoga practices, and time periods. Extracted studies, which were categorized according to the type of intervention (pranayama practice, meditation/relaxation, integrated yoga/asana practice, integrated yoga with physical activity), are presented in Tables 1 to 4, which also include information about study design.

Table 1.

Summary of Studies Reporting Changes in Oxygen Consumption With Pranayama Practice(s).

Study Reference	Population	Study Design	Intervention	Comparators	Metabolic Measures	Cardiorespiratory and Other Measures
Miyamura et al (2002)¹³⁹	Advanced male yoga practitioner (n = 1)	Single practice on a single occasion	Ujjayi breathing at 1 breath/min	Pranayama versus post-pranayama	↑ of 10% in OC during Ujjayi	HR during breathing session 9% higher compared to post
Miles and Behanan (1934)¹¹⁸	Male yoga practitioner (n = 1)	Multiple practices on a single occasion	Ujjayi, Kapalbhati, and Bhastrika breathing	Sitting and reclined postures versus Pranayama	↑ of 33%, 35%, and 30% in OC of during pranayama compared to sitting and 39%, 41%, and 36% compared to reclined
Miles (1964)¹¹⁹	Male yoga practitioner (n = 1)	Multiple practices on multiple occasions	Ujjayi (40 seconds retention at 1.26 breath/min); Kapalbhati (12.5 and 80 breath/min); Bhastrika (21 and 1.3 breath/min)	Baseline versus pranayama practices	↑ of 25% in OC during Ujjayi, 12% during Kapabhati, and 19% during Bhastrika
Rao (1968)⁸⁶	Male yoga practitioner (n = 1)	Single practice on 2 occasions	Ujjayi breathing at 2 different altitudes of 520 m and 3800 m	Baseline versus Ujjayi breathing at low altitude; Baseline breathing versus Ujjayi at high altitude	↑ of 7.7% in OC during Ujjayi with breath rate 1.5 breath/min at low altitude
					↑ of 9.9% in OC during Ujjayi at breath rate 3 breath/min at high altitude
					OC during Ujjayi at high altitude was 16% higher compared to lower altitude
Karambelkar et al (1982)⁸⁷	Male yoga practitioners (n = 8)	Multiple practices on a single occasion	Kapalbhati at 120 breath/min and hyperventilation breathing at 26 breath/min	Baseline breathing versus Kapalbhati breathing and hyperventilative breathing	↑ of 50% in OC and ↑ of 33% in CO₂ exhalation during Kapalbhati	↑ of 209% in MV and ↓ of 63% in VT during Kapalbhati
					↑ of 133% in OC and ↑ of 379% in CO₂ exhalation during hyperventilative breathing	↑ of 538% in MV and ↑ of 250% in VT during hyperventilative breathing
Karambelkar et al (1982)⁸⁸	Male yoga practitioners (n = 3)	Multiple practices on a single occasion	Bhastrika with internal retention (I:R:E = 8:32:16) and external retention (E:R:I = 3:20:10)	Baseline versus Bhastrika breathing with internal retention and external retention	Internal Retention: ↑ of 15% in OC and ↑ of 13% in CO₂ exhalation during Bhastrika
					External retention: ↑ of 17% in OC and ↑ of 32% in CO₂ exhalation during Bhastrika
Frostell et al (1983)¹⁴⁰	Experienced male yoga practitioners (n = 3)	Single practice on a single occasion	Bhastrika at 232 breath/min	Baseline versus pranayama	↑ of 208% in OC and ↑ of 395% in CO₂ exhalation during Bhastrika	↑ of 30 BPM (47%) in HR
						↑ of 88.4 L/min (15-fold increase) in MV
						↑ of 65% in CO
Karambelkar and Bhole (1988)⁸⁹	Male yoga practitioners (n = 7)	Single practice on a single occasion	Kapalbhati at 120 breath/min	Pranayama practices versus baseline	↑ of 51% in OC and ↑ of 34% in CO₂ exhalation during Kapalbhati	↑ of 219% in MV during breathing
Karambelkar et al (1983)⁹⁰	Male yoga practitioners (n = 3)	Multiple practices on a single occasion	Bhastrika with external retention (E:R:I = 3:20:10) and Ujjayi with external retention (E:R:I = 6:12:12)	Pranayama practices versus baseline	↑ of 24% in OC and ↑ of 32% in CO₂ exhalation during Bhastrika
					↓ of 4% in OC and ↓ of 7% in CO₂ exhalation during Ujjayi
Karambelkar et al (1983)⁹¹	Regular and beginner male yoga practitioners (n = 9)	Single practice on a single occasion	Ujjayi breathing with internal (I:R:E = 8:32:16)	Pranayama versus baseline	Significant ↓ of 21% in OC and ↑ of 34% in OC was observed during the same practices, ↓ OC was only seen in the regular yoga practitioners
Danucalov et al (2008)¹³⁸	Experienced yoga practitioners with >3 years of experience (n = 9)	Multiple practices on a single occasion	Slow paced pranayama with extended period of retention (internal retention; I:R:E =1:4:2) and meditation; each phase of 30 minutes	Pranayama versus meditation and baseline	↑ of 20% in OC and ↑ of 25% in CO₂ exhalation during pranayama compared to baseline	↓ of 35% in OC during meditation compared to baseline
					↑ of 84.6% in OC during pranayama compared to meditation
Telles and Desiraju (1991)⁹²	Male yoga practitioners; short breath retention group (n = 5) and long breath retention group (n = 10)	Multiple practices on a single occasion	Ujjayi breathing with 2 different internal retention periods: short retention (I:R:E = 1:4:4) and long retention (I:R:E = 1:1:1)	Baseline versus Pranayama	↑ of 52% in OC (P < .05) during pranayama with short retention (1:1:1); ↓ of 19% in OC (P < .025) during pranayama with long retention (1:4:4)
Telles et al (1996)⁹³	Male yoga practitioners (n = 12)	Multiple practices on 2 occasions	RNB session and normal breathing session (each session of 45 minutes on different days)	Baseline breathing versus post-RNB session and post-RNB session	↑ of 18% in OC (P < .05) after RNB; no significant change after normal breathing compared to baseline	↑ of 9.3% SBP (P < .05) after RNB
						↓ of 60% in GSR after RNB
Prasad et al (2001)⁹⁴	Male yoga practitioners with >3 years’ experience (n = 12)	Multiple practices on a single occasion	ANB for 30 minutes, treadmill walk at 3 km/h (1.9 mph) for 30 minutes, and field walk 1.5 km/30 min	Resting, field walk, and treadmill walk versus ANB	↑ of 150% in OC (P < .01) during ANB compared to resting state OC during ANB 19.6% (P < .05) lower compared to field walk and 37.5% (P < .01) lower compared to treadmill walk
Ray et al (2011)⁹⁵	Male yoga practitioners with >6 years’ experience (n = 20)	Multiple practices on 2 occasions	Hatha yoga session comprising variety of yoga static postures interspersed with Shavasana, pranayamas, and meditation practices; VO_2max session (each session on different days)	Sitting rest (Sukhasana) versus each individual pranayama versus rest sitting	↓ of 16% in OC during Bhastrika; ↑ of 65%, 61%, 33% (Ps < .05) in OC during Raven beak (Kaki Mudra) breathing (P < .05), 61% during I breathing (P < .05), 103 mL/min (33%) during Kapalbhati (P < .05)
Telles et al (1994)⁹⁶	Male yoga practitioners (n = 48)	Four weeks regular practice in multiple groups	Random assignment to RNB (n = 12), LNB (n = 12), or ANB (n = 24); each assigned breathing 4 times daily for 4 weeks	Post-pranayama intervention for versus preintervention	↑ of 37% in OC (P < .05) post-RNB, ↑ of 24% in OC post-LNB, and ↑ of 18% in OC post-ANB compared to preintervention	↓ in body weight after 1 month of pranayama
						↑ of 9.6% and 7% in HR (Ps < .001) post-RNB and post-ANB respectively
						↑ of 150% in GSR (P < .05) post-LNB

Abbreviations: OC, oxygen consumption; HR, heart rate; CO₂, carbon dioxide; MV, minute ventilation; VT, tidal volume; I:R:E, inspiration–retention–expiration; E:R:I, expiration–retention–inspiration; BPM, beats per minute; CO, cardiac output; RNB, right nostril breathing; SBP, systolic blood pressure; GSR, galvanic skin resistance; ANB, alternate nostril breathing; LNB, left nostril breathing.

Table 2.

Summary of Studies Reporting Changes in Oxygen Consumption With Mediation/Relaxation Practice(s).

Study Reference	Population	Study Design	Intervention	Comparators	Metabolic Measures	Cardiorespiratory and Other Measures
Anand et al (1961)⁹⁷	Experienced male yoga practitioner (n = 1)	Single practice on 2 occasions	Stay in airtight box during 2 different days of 10 hours each	Baseline (basal) versus stay in box	↓ of 37.4% and 32% in OC during 2 different sessions	↓ in HR up to 25 BPM during session; HR rose only when ambient O₂ declined to 15% and CO₂ reached to 5% in the pit; OC declined to 50% of BMR (19.5 L/h) on one occasion
Karambelkar et al (1968)⁹⁸	Experienced male yoga practitioners (n = 4)	Single practice on a single occasion	Stay in airtight pit >12 hours and up to 18 hours	Baseline (basal) versus stay in pit	OC during stay in pit lesser than basal condition; subjects remained in pit till ambient O₂ declined to 12% and CO₂ rose to 7%; The maximum stay in pit for 18 hours when ambient CO₂ was 7.7% and O₂ 11.6%	HR and BR rose when ambient CO₂ reached to 5% in pit
Craig Heller et al (1987)⁹⁹	Yogi male (proficient in bhoogarbh smadhi (subterranean stay) (n = 1)	Single practice on a single occasion	Stay in subterranean chamber for 4 hours	Baseline (basal) versus stay in pit	↓ of 40% in OC during the stay in chamber compared to basal baseline measured through gas volume meter
Wallace (1970)¹²⁰	Meditators with >6 months experience (n = 15)	Single practice on a single occasion	Transcendental meditation (TM); 30 minutes meditation session	Baseline versus meditation	↓ of 20% in OC during meditation compared to baseline	↑ of 103% in GSR during onset of meditation
Wallace et al (1971)¹²¹	Meditators with mean 29.4 months experience (n = 36)	Single practice on a single occasion	Transcendental meditation; 30 minutes meditation session	Baseline versus meditation	↓ of 17% in OC (P < .005) and ↓ of 15% in CO₂ exhalation (P < .005) during meditation	↓ in HR and BR (Ps < .05) during meditation; ↑ of 158% in GSR (P < .005) during meditation
Benson et al (1975)¹²²	Meditators with >1 year experience (n = 13)	Single practice on a single occasion	Transcendental meditation; 30 minutes meditation session	Baseline versus meditation	↓ of 5% in OC (P < .001) and ↓ of 6% in CO₂ exhalation (P < .001) during meditation	↓ in HR (P < .01) during meditation
Danucalov et al (2008)¹³⁸	Experienced yoga practitioner with >3 years’ experience (n = 9)	Multiple practices on a single occasion	Slow paced Pranayama with extended period of retention (internal retention—I:R:E = 1:4:2) and meditation; Each phase of 30 minutes	Baseline versus meditation and pranayama	↓ of 35% in OC (P < .05) and ↓ 31.2% in CO₂ exhalation (P < .05) during meditation compared to baseline; ↓ of 49% in OC during meditation compared to pranayama	↓ of 8% in HR (P < .05) during meditation compared to baseline and pranayama; ↑ of 20% in OC during pranayama compared to baseline
Fenwick et al (1977)¹³⁴	Meditators with >22 months experience (n = 11) and nonmeditators (n = 8)	Multiple practices on a single occasion	Transcendental meditation (TM) and listening music	Baseline versus meditation and listening to music in meditators and nonmeditators; comparison between groups	Nonsignificant drop in OC and CO₂ exhalation during meditation in meditators and nonmeditators; nonsignificant difference in reduction of OC between meditation and listening music; nonsignificant difference between groups	No evidence of hypometabolism during meditation in both the groups
Warrenburg et al (1980)¹²³	Regular meditators with mean 3.4 years’ experience (n = 9); regular relaxation practitioners with mean 6.4 years’ experience (n = 9); nonpractitioners (n = 9)	Multiple practices on a single occasion	Transcendental meditation (TM); progressive muscle relaxation (PMR); nonpractitioner—listening music	Control periods of closed eyes and reading book versus intervention; comparison between groups	↓ in OC during TM 4%, during PMR 3.5%, in regular practitioners, and 8.3% in nonpractitioners (Ps < .01) compared to periods of control; nonsignificant difference between groups	↓ HR during meditation or relaxation (P < .01)
Kesterson and Clinch (1989)¹²⁴	Advanced meditators with mean 28 years experience (n = 33); nonmeditators (n = 10)	Multiple practices on a single occasion	Transcendental meditation (TM); nonmeditators—eyes closed relaxation	Baseline versus intervention; comparison between the groups	Similar significant drop in OC (P < .002) during TM and relaxation; nonsignificant difference between groups	No traces of hypometabolism in either group
Telles et al (1995)¹¹⁷	Male meditators with >5 years experience (n = 7)	Multiple practices on 2 occasions	Aum meditation session and sitting relaxed session (each session of 20 minutes on different days)	Baseline rest versus postmeditation and eyes closed relaxation	Nonsignificant change in OC in postmediative session compared to baseline	↓ in HR (P < .001) during meditation
Vempati and Telles (1999)¹⁰¹	Male yoga practitioner with mean 23.9 months experience (n = 40)	Multiple practices on 2 occasions	Yoga-based isometric relaxation and supine rest (each session of 10 minutes on different days)	Baseline rest versus postrelaxation and supine rest	↓ of 23% (P < .001) in OC in post yoga relaxation compared to baseline; ↓ of 7% in OC after supine rest	↓ of 20.6% in BR (P < .01) post -yoga relaxation
Vempati and Telles (2002)¹⁰⁰	Male yoga practitioner with mean 30.2 months experience (n = 35)	Multiple practices on 2 occasions	Yoga-based guided relaxation session and supine rest session (each session of 10 minutes on different days)	Baseline rest versus postrelaxation and supine rest	↓ of 25.2% in OC (P < .001) in post-yoga relaxation compared to baseline; ↓ of 7% in OC after supine rest	↓ of 9.7% in HR (P < .001), ↓ in LF (P < .05), ↑ in HF (P < .05) after relaxation compared to baseline
Ray et al (2011)⁹⁵	Male yoga practitioners >6 years’ experience (n = 20)	Multiple practices on 2 occasions	Hatha yoga session—comprising variety of yoga static postures interspersed with Shavasana, pranayamas, and meditation practices; VO_2max session (each session on different days)	Rest sitting (Sukhasana) versus meditation and Aum meditation	↓ of 15%in OC (P < .05) during meditation and 4% during Aum meditation compared to Sukhasana	↓ of 37% in BR (P < .05) during Aum meditation
Throll (1982)¹³⁶	Healthy nonpractitioner males (n = 39)	15 weeks of regular practice, multiple group	Meditation group (n = 21); transcendental meditation, relaxation group (n = 18); progressive muscle relaxation	Baseline versus immediately after practice of first session and then after 5, 10, and 15 weeks apart	Meditators displayed greater reduction in OC during the practice; reduction in OC more prominent in relaxation overtime of 15 weeks compared to meditation	Reduction in HR in meditation group prominent (P < .05) compared to relaxation over time

Abbreviations: OC, oxygen consumption; HR, heart rate; BPM, beats per minute; CO, carbon dioxide; BMR, basal metabolic rate; BR, breath rate; GSR, galvanic skin resistance; I:R:E, inspiration–retention–expiration; LF, low frequency; HF, high frequency.

Table 3.

Summary of Studies Reporting Changes in Oxygen Consumption With Asana, Integrated Practice(s).

Study Reference	Population	Study Design	Intervention	Comparators	Metabolic Measures	Cardiorespiratory and Other Measures
Rao (1962)⁸⁵	Male yoga practitioners (n = 6)	Single practice on a single occasion	Head stand posture	Baseline recumbent and standing erect versus head stand posture	↑ of 68% and 48% in OC during headstand posture compared to recumbent position and standing erect, respectively
Rai and Ram (1993)¹⁰³	Male yoga practitioners (n = 10)	Single practice on a single occasion	Virasana (hero pose); Subgroup 1—with resting breath rate >10 breath/min (n = 6); Subgroup 2—with resting breath rate <5 breath/min (n = 4)	Baseline Shavasana versus Virasana	Subgroup 1: ↑ of 159% in OC (P < .005) and ↑ of 223% in CO₂ exhalation (P < .01) during Virasana in group with BR >10 breath/min; Subgroup 2: ↑ of 163% in OC (P < .05) and ↑ of 166% in CO₂ exhalation during Viransana in group with BR <5 breath/min	↑ of 60% (P < .0005) and 43% (P < .001) in HR in subgroups 1 and 2, respectively
Rai et al (1994)¹⁰²	Male yoga practitioners (n = 10)	Single practice on a single occasion	Siddhasana (accomplished pose); Subgroup 1—with resting breath rate >10 breath/min (n = 6); Subgroup 2—with resting breath rate <5 breath/min (n = 4)	Baseline Shavasana versus Siddhasana	Subgroup 1: ↑ of 27% in OC (P < .01) and ↑ of 31% (P < .01) in CO₂ exhalation during Siddhasana in group with >10 breath/min; Subgroup 2: ↑ of 21% in OC and ↑ of 25% in CO₂ exhalation during Siddhasana in group with >5 breath/min	↑ of 13% (P < .01) and of 15% (P < .001) in HR in subgroups 1 and 2, respectively
Sinha et al (2004)¹⁰⁴	Male yoga practitioners (n = 21)	Single practice on a single occasion	Sun salutation (SS)—12 dynamic postures preceded and followed by Shavasana	Comparison between each individual posture of SS and Shavasana	↑ of 207% in OC during complete session of SS compared to Shavasana; ↑ of 383% during 8th pose (Cobra) compared to Shavasana; OC higher (P < .05) during backward bending poses (2nd, 4th, 5th, and 8th poses) compared to forward bending poses (3rd and 11th)	HR range—83.5 BPM to 101.6 BPM during entire SS compared to 60.2 BPM during Shavasana
Blank (2006)¹²⁵	Female yoga practitioners (n = 15)	Single practice on a single occasion	Iyenger yoga posture sequences—warm-ups, 20 individual postures and releasing poses with Shavasana	Comparison between each individual posture and postures divided in sets (back arch, inversion, standing, supine, and seated) versus Shavasana	↑ of OC during standing, back arc, and inversion poses (P < .05) compared to supine and seated posture; ↑ of 300% of OC (P < .05) during warrior pose III compared to Shavasana; ↑ of 144% in OC during 65 minutes yoga session compared to Shavasana	Back arch poses 75% of HR_max
Hagins et al (2007)¹²⁶	Yoga practitioners with >1 year experience in yoga; 2 males, 28 females (n = 20)	Multiple practices on a single occasion	Ashtanga yoga session of 56 minutes—Warm-up, sun salutation, and non-sun salutation poses; mild and moderate submaximal exercise—treadmill walk at 2 mph and 3 mph	Baseline rest and mild to moderate exercise versus yoga session; sun salutation versus non-sun salutation poses	↑ of 100% in OC (P < .0001) during yoga session compared to rest; OC 14% lower during yoga sequence compared to mild exercise and 33% lower to moderate exercise (Ps < .0001); OC 25% higher (P < .001) during sun salutation compared to non-sun salutation poses	↑ of 31% in HR (P < .0001) during yoga compared to rest; yoga sequence 49.4% of HR_max; HR 15% higher during sun salutation compared to non-sun salutation poses
Telles et al (2000)¹⁰⁵	Male yoga practitioner with >3 months experience (n = 40)	Multiple practices on 2 occasions	Cyclic meditation (CM) session and Shavasana session (each session on different days)	Baseline rest versus postpractice session of CM and Shavasana	↓ of 32% in OC (P < .001) post-CM; ↓ of 10% in OC (P < .05) post-Shavasana compared to baseline	↓ of 28% (P < .001) and 15% (P < .05) in BR during postsession in CM and Shavasana, respectively
Sarang and Telles (2006)¹⁰⁶	Male yoga practitioner with >3 months experience (n = 50)	Multiple practices on 2 occasions	Cyclic meditation session (CM) (divided into 4 phases) and Shavasana session (each session on different days)	Baseline rest versus CM session and Shavasana session; baseline rest versus postpractice session of CM and Shavasana	↑ of 31.3% in OC (P < .001) during active phases of CM; ↓ of 19.4% in OC (P < .001) post-CM compared to baseline; ↓ of 7% in OC (P < .001) post-Shavasana; nonsignificant change in OC during Shavasana compared to baseline	↑ up to 21% in BR (P < .001) during CM and ↓ of 7% (P < .05) in BR post-CM compared to baseline
DiCarlo et al (1995)¹³²	Yoga practitioners with >1 year experience (n = 10)	Multiple practices on 2 occasions	Hatha yoga—12 standing postural sequence session; submaximal exercise session treadmill walk at 4 mph and VO_2max session (each session on different days)	Submaximal exercise and VO_2max session versus Hatha yoga routine session	OC 26% lower during yoga sequences (P < .05) compared to submaximal exercise in first 8th minute and remained lower during complete session; yoga session 34% of VO_2max and submaximal exercise 46% of VO_2max	HR 4% higher in during yoga sequence (P < .05) compared to submaximal exercise in 8th minute and remained higher during complete yoga session
Carroll et al (2003)¹²⁷	Yoga practitioners with >3 months experience (n = 13)	Multiple practices on 2 occasions	Vinyasa yoga sequences and VO_2max	VO_2max versus Vinyasa yoga	Yoga session >50% of VO_2max	Yoga session >77% of HR_max
Clay et al (2005)¹³¹	Yoga practitioners with >1 month experience (n = 30); 2 males, 28 females	Multiple practices on 2 occasions	Hatha yoga session—Warm-ups, sun salutation, non-sun salutation, and cool down poses; submaximal exercise—treadmill walk at 3.5 mph and VO_2max session (each session on different days)	Chair sitting, submaximal exercise and VO_2max session versus Hatha yoga session	↑ of 114% in OC (P < .05) during yoga session compared to chair sitting; OC 54% lower (P < .05) during yoga session compared to submaximal exercise; yoga session 14.5% and submaximal exercise 44.8% of VO_2max; OC 82% higher (P < .05) during sun salutation compared to non-sun salutation	↑ of 24% in HR (P < .06) during yoga session compared to chair sitting; HR 21% lower (P < .05) during yoga session compared to submaximal exercise; HR 20% higher (P < .05) during sun salutation compared to non-sun salutation
Buranruk et al (2010)¹³⁷	Middle aged non-yoga practitioners (n = 17)	Multiple practices on 2 occasions	Thai yoga session—warm-ups, sitting, standing, and lying poses; VO_2max (each session on different days)	VO_2max session and baseline rest versus Thai yoga session; calorimetry	↑ of 133% during yoga session compared to rest; yoga session 35.5% of VO_2max; OC 46% higher (P < .0001) during standing poses compared to sitting	↑ of 16.6% in HR during Thai yoga compared to rest; HR during yoga sequence 50% of HR_max; HR 10.6% higher (P < .0001) during standing poses compared to sitting
Ray et al (2011)⁹⁵	Male yoga practitioners with >6 years’ experience (n = 20)	Multiple practices on 2 occasions	Hatha yoga session—comprising variety of yoga static postures interspersed with shavasana, pranayamas, and meditation practices; VO_2max session (each session on different days)	VO_2max session and shavasana versus individual yoga static postures	↑ of 160% in OC (P < .05) during plough pose-2; ↑ of 156% in OC (P < .05) during bow pose compared to shavasana; Bow, plough-1, plough-2, and shoulder stand pose 26.5%, 25.9%, 24.6%, 22.7%, respectively, of VO_2max; shavasana 9.9% of VO_2max	↑ of 108% in BR (P < .05) during ploughs 1 and 2 compared to shavasana

Abbreviations: OC, oxygen consumption; CO₂, carbon dioxide; BR, breath rate; HR, heart rate; BPM, beats per minute.

Table 4.

Summary of Studies Reporting Changes in Oxygen Consumption With Yoga and Physical Activity.

Study Reference	Population	Study Design and Duration	Intervention	Comparators	Metabolic Measures	Cardiorespiratory and Other Measures
Salgar et al (1975)¹⁰⁷	Healthy males (n = 38)	Multiple practices on single occasion	6 months of regular lotus posture (n = 10); resistance training (n = 12); sedentary lifestyle (n = 16)	Comparison between groups during mild and moderate level ergometer exercise	At mild-level exercise the OC was lowest in lotus group followed by exercisers and nonexercisers; at moderate-level exercise OC lowest in exercisers followed by lotus and nonexerciser groups
Bhatnagar et al (1978)¹⁰⁸	Healthy non-yoga practitioners (n = 20)	6-Month cohort study of multiple practices	Regular integrated yoga practices	Pre-yoga intervention submaximal exercise versus fixed intensity submaximal exercise after 1, 3, and 6 months of yoga practice	Progressive increase in OC during submaximal exercise (P < .05) in 3 and 6 months compared to pre-intervention; no significant increase after 1 month	↓ in resting body core temperature (P < .05, P < .001, P < .001) in 1, 3, and 6 months compared to pre-intervention
Joseph et al (1981)¹⁰⁹	Healthy male non-yoga practitioners (n = 10)	3-Month cohort study of multiple practices	Regular integrated yoga practices	Pre-yoga intervention rest versus post-yoga intervention rest	Nonsignificant decrease in resting OC	↓ of 7.8% in HR (P < .001); ↓ in SBP/DBP (P < .01); ↓ in blood glucose (P < .05) and blood cholesterol (P < .01)
Raju et al (1986)¹¹⁰	Non-yoga practitioners (n = 12)	3-Month cohort study of multiple practices	Regular integrated yoga practice	Pre-yoga intervention rest versus post-yoga intervention rest; Pre-yoga intervention submaximal exercise versus sub-maximal exercise after 20 days and 3 months of yoga practice	Nonsignificant change in resting OC in either gender; ↓ of 41% in OC (P < .05) during submaximal exercise after 20 days and ↓ of 36% in OC (P < .05) during submaximal exercise after 3 months in males only	↓ of 65.5% in blood lactate (P < .05) in males at same exercise workload after 3 months; no significant changes in females
Balasubramanian and Pansare (1991)¹¹⁶	Healthy non-yoga practitioners (n = 17)	6-Week cohort study of multiple practices	Integrated yoga practice	Pre-yoga intervention VO_2max versus post-yoga intervention VO_2max	↑ of 17% in VO_2max (P < .005)
Raju et al (1997)¹¹¹	Healthy female non-yoga practitioner (n = 6)	4-Week cohort study of multiple practices	Integrated yoga practice	Pre-yoga intervention VO_2max versus exercise versus post-yoga intervention VO_2max	↓ of 14% in OC (P < .05) per unit of work load; ↑ of 21% in maximal work load (P < .05) in post-yoga intervention compared to pre-yoga intervention	↓ of 6% in HR (P < .05) post-yoga intervention; ↓ in body fat and weight (P < .05)
Tran et al (2001)¹²⁸	Healthy non-yoga practitioners (n = 10)	8-Week cohort study of multiple practices	Integrated yoga session	Pre-yoga intervention VO_2max versus post-yoga intervention VO_2max	↑ of 10% in VO_2max (P < .01)	↑ in muscular strength (P < .05), muscular endurance (P < .01), and flexibility (P < .001)
Ramos-Jiménez et al (2011)¹⁴²	Female, middle-aged, and old yoga practitioners with >3 years’ experience (n = 13)	11-Week cohort study of multiple practices	Integrated intensive yoga training (middle-aged practitioners with mean age 43.2 years = 4; older practitioners with mean age 62.2 years = 9)	Pre-yoga intervention VO_2max versus post-yoga intervention VO_2max	↑ of 3% in VO_2max (P < .05) in middle-aged group and ↑ of 17% in VO_2max (P < .05) in older group	Increase in HR_max (P < .05) in both groups; improvement in lipid profile and blood glucose and BMI (Ps < .05) in both groups
Raju et al (1994)¹¹²	Healthy male non-yoga practitioners (n = 28)	24-Month NRCT of multiple practices	Yoga group—Pranayama and shavasana along with regular sports workouts (n = 14); Control—Regular sports workouts (n = 14) (each group further subgrouped into Phases 1 and 2 of submaximal (n = 12) and maximal exercise (n = 16) of duration 12 months and 24 months, respectively)	Pre-intervention rest versus post-yoga intervention rest (phases 1 and 2); pre-intervention submaximal and maximal exercise versus post-yoga intervention submaximal and maximal exercise	Phase 1—↓ of 38% in OC at resting state in yoga group; ↓ of 51% in OC (P < .05) per unit work load with submaximal exercise in yoga group after intervention; no change in controls either in rest or during exercise; Phase 2—No change in resting OC in either yoga or control group; ↓ of 34% in OC (P < .05) per unit work load with maximal exercise in yoga group after intervention; no change in control	Phase 1—↓ of 49% in resting blood lactate (P < .01) in yoga group; Phase 2—↓ of 37% in resting blood lactate (P < .05) in yoga group; ↓ of 61% in exercise blood lactate after 24 months compared to pre-intervention in yoga group
Ray et al (2001)¹¹⁵	Healthy male non-yoga practitioners (n = 28)	6-Month RCT of multiple practices	Yoga group—integrated yoga practices (n = 17); physical training as per army program (n = 11)	Pre-intervention VO_2max versus postintervention VO_2max	↑ of 6.7% in VO_2max (P < .05) in yoga group; no change in physical training group	↓ in body fat and body weight (Ps < .01) in yoga group
Nayar et al (1975)¹¹³	Healthy male non-yoga practitioners (n = 53)	12-Month RCT of multiple practices	Yoga group—integrated yoga with regular physical training (n = 18); Athletic group—athletics with regular physical training (n = 17); Control—regular physical training (n = 18)	Pre-intervention rest versus postintervention rest; pre intervention submaximal versus postintervention submaximal exercise	Nonsignificant change in OC at rest in either group; nonsignificant changes in OC during submaximal exercise in either group	↑ of 29% in vital capacity (P < .01) and 5% in FEV₁ (P < .05) in yoga group; ↑ of 46% in breath-hold time (P < .01) in yoga group
Selvamurthy et al (1988)¹¹⁴	Healthy male non-yoga practitioners (n = 30)	6-Month RCT of multiple practices	Yoga group—integrated training (n = 15); Physical training (PT) group—running, games, flexibility, and pull-ups (n = 15)	Pre-yoga intervention submaximal exercise versus post-yoga intervention submaximal exercise	↓ of 5.7% in OC (P < .05) in yoga group; nonsignificant change in PT group	↓ of 7% in HR (P < .01) in yoga group
Bowman et al (1997)¹³³	Sedentary healthy elderly subjects >62 years (n = 40)	6-Week RCT of multiple practices	Yoga group—integrate yoga (n = 20); aerobic group—bicycle-based aerobic training (n = 20)	Pre-yoga intervention submaximal exercise versus post-yoga intervention with submaximal exercise	↑ of 13% in VO_2max (P < .01) in yoga group and ↑ of 24% in VO_2max (P < .01) in aerobic group	↓ of 11.6% in HR (P < .05) in yoga group; no change in aerobic group; ↑ in baroreflex sensitivity (P < .01) in yoga group; no significant change in HRV in either groups
Pullen et al (2008)¹³⁰	Patients with congestive heart failure (CHF) (n = 19)	8-Week RCT of multiple practices	Yoga group—integrated yoga practices along with standard medical therapy (n = 9); Control—standard medical therapy with general awareness (n = 10)	Pre-intervention VO_2max versus postintervention VO_2max	↑ of 17% in VO_2max (P < .02) in yoga group; no change in controls	Improvement of 25.7% in quality of life scores (P < .005) in yoga group
Tracy and Hart (2012)¹²⁹	Sedentary healthy non-yoga practitioners (n = 21)	8-Week RCT of multiple practices	Bikram yoga—26 series of postures in heated (35°C to 40°C) humidified studio (n = 10); waitlist control (n = 11)	Pre-yoga intervention VO_2max versus post-yoga intervention VO_2max	No change in VO_2max after yoga training	↑ of 23.8% in sit and reach score (P < .001) and shoulder flexibility (P < .05) with yoga
Chaya et al (2006)⁷⁰	Non-yoga (NY) and regular yoga practitioners (YP) with >6 months experience (n = 104)	Multiple practices on a single occasion	YP—regular integrated yoga practice (n = 55); NY (n = 49)	Yoga practitioners versus non-yoga practitioners at rest (basal state)	Basal OC—19.3% less in female YPs and 10.7% less in male YPs (Ps < .001) compared to NYs; Basal CO₂—12.7% less in female YPs and 14.3% less in male YPs (Ps < .05) compared to NYs; BMR in YP 15% less (P < .001) in YP compared to NY and 13% less than the predicted by WHO/FAO/UNU	BR 19.6% less (P < .001) in female YPs and 19% (P < .001) in male in YPs compared to NYs
Chaya and Nagendra (2008)⁷¹	Non-yoga (NY) and regular yoga practitioners (YP) with >6 months experience (n = 88)	Multiple practices on a single occasion	YP—regular integrated yoga practice (n = 51); NY (n = 37)	Yoga practitioners versus non-yoga practitioners at rest at 6 am (basal) and 9 pm (pre-sleep)	Basal OC—22% less (P < .005) in female YPs and 10.7% less (P < .05) in male YPs compared to NY females and males, respectively; Pre-sleep OC—17% less in female YPs and 6.7% in male YPs (nonsignificant) compared to NY females and males, respectively; Basal CO₂—15.3% less in female YPs and 14.8% less in male YPs (Ps < .05) compared to NYs; Pre-sleep CO₂—13.2% less in female YPs and 8.3% in male YPs compared to NYs	BR 23.3% less (P < .005) in female YPs and 15.6% less (P < .05) in male YPs during morning compared to NYs

Abbreviations: OC, oxygen consumption; HR, heart rate; SBP, systolic blood pressure; DBP, diastolic blood pressure; BMI, body mass index, NRCT, nonrandomized controlled trial; RCT, randomized controlled trial; FEV₁, forced expiratory volume in 1 second; HRV, heart rate variability; CO₂, carbon dioxide exhalation; BMR, basal metabolic rate; BR, breath rate.

Of the total studies, 35 studies were published from India,^{70,71,85

–117} 15 from the United States,^{118

–132} 2 from the United Kingdom,^133,134 and 1 each from Mexico,¹³⁵ New Zealand,¹³⁶ Thailand,¹³⁷ Brazil,¹³⁸ Japan,¹³⁹ and Sweden.¹⁴⁰ Most studies reported assessing direct measurement of respired gases for measuring oxygen consumption using indirect calorimetry techniques, whether through open circuit, closed circuit, bag system, or respiratory chamber method. Some studies derived oxygen consumption through the standard equations, that is, oxygen consumption was predicted through regression equation with measures of heart rate and oxygen consumption of submaximal exercise,⁹⁴ while VO₂ max was predicted through achieved workload and using standard formula from the American College of Sports and Medicine.^116,130 Oxygen consumption was reported to both increase and decrease with different yoga practices. Increases in oxygen consumption ranged from 7.7% with Ujjayi breathing to 383% during cobra pose (Tables 1 and 3). Studies also report decreases in oxygen consumption, with slow yoga breathing techniques and meditation practices ranging from a 3.7% decrease during Om meditation to a 40% decrease in an advanced yogi during meditation in an airtight pit (Table 2). Basal oxygen consumption is also reported to be up to 15% less in regular yoga practitioners compared to nonpractitioners, and oxygen consumption during submaximal exercise is reported to decrease by 36% after 3 months of regular yoga practice (Table 4).

Pranayama Practices and Oxygen Consumption

Table 1 summarizes 16 pranayama (yogic breathing) studies that include a total of 143 participants and report wide variations in oxygen consumption. While oxygen consumption was seen to increase with most breathing practices performed at both fast (232 breath/min) and slow (1 breath/min) rates (Table 1), a decrease in oxygen consumption from rest was also seen in some slow breathing practices. The highest increase in oxygen consumption was seen with extremely rapid Bhastrika breathing, which involves rapid, forced thoracic inhalation and exhalation. When Bhastrika was performed at a rate of 232 breath/min by 3 advanced practitioners, oxygen consumption was reported to increase by 208%,¹⁴⁰ and increases in oxygen consumption of 30%, 24%, 22%, 17%, and 15% is reported with Bhastrika performed at different rates and retention periods.^{88,90,118,119} Increases in oxygen consumption of 12%¹¹⁹ to 50%⁸⁷ are also reported with Kapalbhati breathing, which involves forced rapid exhalation. Unilateral nostril breathing (alternate nostril breathing, right nostril breathing, and left nostril breathing) are reported to increase oxygen consumption with a 150% increase during alternate nostril breathing⁹⁴ and increases of 37%⁹⁶ to 18%^93,96 reported immediately after alternate nostril breathing, right nostril breathing, and left nostril breathing practices.

Oxygen consumption is also reported to increase with some slow yoga breathing. Ujjayi breathing, which involves controlled slow, deep breathing with long inhalation and exhalation and gentle contraction of the glottis creating a soft snoring sound,¹⁴¹ has been consistently reported to increase oxygen consumption, even at extremely slow rates. An increase of 10% is reported in a single advanced practitioner while practicing Ujjayi at a rate of 1 breath/min,¹³⁹ while further studies report increases in oxygen consumption of 25% and 52% during Ujjayi with a 40-second retention (rate of 1.26 breath/min)¹¹⁹ or with an inspiration–retention–expiration ratio of 1:1:1.⁹² An increase in oxygen consumption was also reported with Ujjayi performed at different altitudes, with a 16% greater oxygen consumption observed in a single practitioner at 3200 m elevation practicing Ujjayi breathing at 3 breath/min compared to practicing Ujjayi breathing at 520 m elevation at 1.5 breath/min.⁸⁶ An increase in oxygen consumption to 17% has also been reported in advance yoga practitioners during slow paced breathing with and inspiration–retention–expiration ratio of 1:4:2.¹³⁸

Only 4 studies (Table 1) report decreases in oxygen consumption with pranayama. A decrease in oxygen consumption of 4%, 21%, and 19% is reported during slow Ujjayi breathing at rates of 2 breath/min,⁹⁰ 1.4 breath/min,⁹¹ or with an inspiration–retention–expiration ratio of 1:4:4.⁹² A decrease in oxygen consumption of 16% is also reported during Bhastrika breathing at 12 breath/min.⁹⁵

Yoga Meditation, Relaxation Practices, and Oxygen Consumption

Table 2 summaries 15 studies with a total of 310 participants that consistently report reduced oxygen consumption during different meditation and relaxation practices. Two studies of yogic relaxation practices report 25.2% and 23% reductions in oxygen consumption compared to rest.^100,101 Transcendental meditation is also reported to produce reductions of oxygen consumption from rest, with 3 separate studies reporting reductions of 20%, 17%, and 5%.^120
–122 Reductions in oxygen consumption from rest of 15% and 3.7% are also reported during 2 to 3 minutes of meditation.⁹⁵

Studies comparing meditation with non-yogic relaxation techniques shows modest or no difference between interventions. Four studies report no difference in oxygen consumption between groups practicing Transcendental and those practicing a control relaxation intervention,^{123,124,134,136} while a further study reports no significant reduction in oxygen consumption from baseline rest during either after Om meditation or relaxed sitting, despite reported reductions in heart rate and increases in galvanic skin response.¹¹⁷

Among the studies reporting reductions in oxygen consumption, the most dramatic reductions were seen in 2 studies involving advance yoga practitioners, with one study reporting reductions in oxygen consumption of 40% below rest during a 4 hour stay in an air tight subterranean chamber⁹⁹ and another study reporting reductions of 32% and 37% below rest during 2 separate 10-hour stays in an airtight box.⁹⁷ Reductions in oxygen consumption of around 35% below rest are also reported during meditation in a group of experienced yogis (n = 9).¹³⁸ An early study with 3 advanced yoga practitioners further reports that during a prolonged stay in an airtight pit, advanced meditators could tolerate ambient oxygen levels of 12.2% and carbon dioxide levels of 7.3%.⁹⁸

Asana/Integrated Yoga Practices and Oxygen consumption

Table 3 presents 13 studies with a total of 272 subjects that consistently report increases in oxygen consumption with different yoga asanas (postures). The most dramatic increase was seen in a group of 21 male practitioners who experienced a 383% increase in oxygen consumption while performing cobra pose.¹⁰⁴ Increases in oxygen consumption were also reported with warrior III pose (300%),¹²⁵ plough pose 2 (160%),⁹⁵ Hero pose (159%),¹⁰³ headstand pose (68%),⁸⁵ and accomplished pose (27%).¹⁰²

Over the course of a yoga session, oxygen consumption has been reported to increase by 100% with Ashtanga yoga,¹²⁶ 114% with Hatha yoga,¹³¹ 133% with Thai yoga,¹³⁷ and 144% with Iyenger yoga.¹²⁵ Three studies have examined oxygen consumption during Sun Salutation (a dynamic sequence of 12 postures) and report that oxygen consumption increased 205% above resting levels¹⁰⁴ and 25%¹²⁶ and 81%¹³¹ above the levels during static postures.

The reported increases in oxygen consumption seen with yoga practices are less than observed with maximal or submaximal exercise. Oxygen consumption during Thai yoga is reported to be 35.5% of VO_2max,¹³⁷ Vinyasa yoga, 50%,¹²⁷ bow posture, 26.5%, and Shavasana (supine pose), 9.9%,⁹⁵ of VO_2max. Similarly, Iyenger, Ashtanga, and Hatha yoga sequences have been shown to be of lower intensity than submaximal exercise, having oxygen consumption that is 26%, 33%, and 54% lower than oxygen consumption during treadmill walking at 4 mph,¹³² 3 mph,¹²⁶ or 3.5 mph,¹³¹ respectively.

While oxygen consumption is reported to increase during a yoga session, there are reports that oxygen consumption may fall below presession levels immediately after certain practices. During cyclic meditation, which involves a series of postural sequences interspersed with periods of relaxation, oxygen consumption is reported to increase by up to 55% during the active phase and then fall to 19% below presession levels in the immediate postsession period.¹⁰⁶ Similar results are reported in a further study, which reports a 32% decrease in oxygen consumption immediately after cyclic mediation.¹⁰⁵

Regular Yoga Practice, Physical Activity, and Oxygen Consumption

Table 4 presents 16 studies involving 516 participants that measured oxygen consumption at rest or during physical activity (submaximal and maximal) after 1 month to 24 months of integrated yoga practice (including asana, pranayama, and relaxation) along with 2 studies comparing oxygen consumption at rest in yoga and non-yoga practitioners^70,71 and 1 study comparing oxygen consumption between groups who regularly practiced lotus posture and groups of regular exercisers or healthy sedentary subjects.¹⁰⁷

Most of these studies report that regular yoga practice leads to progressive reductions in oxygen consumption over time. In a 3-month cohort study, yoga practice was found to reduce oxygen consumption during submaximal exercise by 36% compared to baseline levels.¹¹⁰ A randomized trial involving male soldiers found that 6 months of yoga practice (n = 15) reduced oxygen consumption during submaximal exercise by 5.7% (P < .05) compared to no change in a physical training group (n = 15),¹¹⁴ while a nonrandomized study reports that 12 months of regular yoga practice with regular sports activity improved submaximal work efficiency in athletes with 51% greater work output per liter of oxygen consumed, compared to no change in regular sports activity group.¹¹²

VO_2max was also reported to increase with regular yoga practice, ranging from 6 weeks to 6 months in diverse populations. A 3% increase in VO_2max is reported in the cohort of middle-aged yoga practitioners who practiced intensive yoga for 11 weeks¹⁴² and 7% increase in VO_2max in a cohort of yoga navies who practiced integrated yoga for 8 weeks.¹²⁸ Similarly, up to 7% increment of VO_2max is reported in a randomized trial of 6 months in male soldiers with integrated yoga (n = 17) compared to no change in a physical training group (n = 11),¹¹⁵ and a 13% (P < .01) increase in VO_2max is reported in elderly subjects in a randomized trial after 6 weeks of yoga with practice (n = 20), similar to significant increase with aerobic training (n = 20).¹³³

Increases in VO_2max of approximately 17% are also reported after yoga practice in 2 cohort studies including a 6-week study of healthy subjects (n = 17)¹¹⁶ and an 11-week study of elderly yoga practitioners (n = 9).¹⁴² Similar increases in oxygen consumption are reported in an 8-week randomized controlled trial of patients with congestive heart failure who practiced yoga (n = 9), compared to no change in a standard medical therapy group (n = 10).¹³⁰ A further cohort study of female physical trainers found that 1 month of yoga practice led to 14% greater maximal work efficiency.¹¹¹ Maximal work efficiency was also seen to improve in a nonrandomized controlled trial by 34% in athletes after 24 months of regular yoga practice compared to a control group practicing physical exercise.¹¹²

Not all the studies report improvement in oxygen consumption or work efficiency with regular yoga practice. A 12-month randomized study reports no change in oxygen consumption during submaximal exercise in either a yoga or aerobic training group.¹¹³ In another randomized study, no change in VO_2max is reported after 8 weeks in a yoga practice group (n = 10) compared to a no-intervention control group (n = 11).¹²⁹ Similarly, two 3-month cohort studies report no change in oxygen consumption at rest after regular yoga practice,^109,110 and similar results are reported in a 12-month randomized controlled trial.¹¹³ In contrast to most of the above-mentioned studies, one small cohort study reported increased oxygen consumption during submaximal exercise after 6 months of regular yoga practice in healthy subjects despite an observed reduction in resting core body temperature.¹⁰⁸

When examining oxygen consumption at rest, 2 studies report basal oxygen consumption to be significantly less in regular yoga practitioners compared to non-yoga practitioners. One study⁷⁰ reports that regular yoga practitioners had basal metabolic rate 13% less than predicted based on the FAO/WHO/UNU equation¹⁴³ and that oxygen consumption during basal conditions was significantly less in regular yoga practitioners compared to non-yoga practitioners. Similar results were reported in the second study, which report that regular yoga practitioners had basal metabolic rate that was 17.8% less than non-yoga practitioners.⁷¹

Discussion

Studies published to date suggest that yoga practices can have profound metabolic effects producing both significant increases and decreases in oxygen consumption. Like other physical activity, physical yoga postures can increase oxygen consumption dramatically, yet yoga practices do not involve maximal exertion. For example, dynamic postures such as cobra pose are reported to increase oxygen consumption by 383% or around 1220 mL/min, which is less than half that produced with maximal exercise in the average untrained healthy male.³ The most dramatic change seen with yoga is reduction of oxygen consumption, with reports of yoga practices downregulating the sympathetic nervous system and producing modest reductions in oxygen consumption comparable to practices such as progressive muscle relaxation, closed eyes relaxation, and listening to music,^{123,124,134,136} as well as reports of dramatic reductions up to 40%.⁹⁹ This suggests that yoga may downregulate the hypothalamic–pituitary–adrenal axis and the sympathetic activity and therefore promote relaxation and stress relief.

Regular yoga practice also appears to have a training effect, with regular yoga practitioners consistently showing significant reductions in oxygen consumption during normal physical activity compared to non-yoga practitioners. Thus, unlike other physical training, which generally increases resting metabolic rate,^144,145 regular yoga practice is reported to decrease resting oxygen consumption to levels lower than predicted by the FAO/WHO/UNU equation.⁷⁰ This may be due to regular physical training producing an increase of muscle mass, which requires greater oxygen consumption supply at rest, whereas yoga training may instead increase efficiency of mitochondrial oxidative phosphorylation and reduce oxygen demand.

Yoga practices are also reported to shift lactate threshold (anaerobic threshold) and improve work efficiency, indicating aerobic capacity and reduced muscle fatigue to a greater degree compared to physical activity.¹¹² These results are supported by a randomized crossover trial documenting reduction in blood lactate, heart rate, and blood pressure with regular yoga practice.¹⁴⁶

A recent review of yoga and exercise found that yoga may be as effective as or better than aerobic exercise at improving a variety of health-related outcome measures in both healthy and diseased populations.¹⁴⁷ Despite multiple studies demonstrating the benefits of yoga in various clinical conditions, only one small study examined the effects of yoga and oxygen consumption in a clinical population. This study reported increased aerobic capacity (VO_2max) in patients with congestive heart failure after practicing yoga postures, breathing techniques, and meditation over a period of 8 weeks.¹³⁰ Previous research also suggests that instruction on respiration and relaxation, in addition to physical exercise, enhances respiratory sinus arrhythmia and slows heart rate and breath rate in myocardial infarction patients during rehabilitation¹⁴⁸ and that slow rhythmic respiration can be used as a therapeutic tool for anxiety,¹⁴⁹ hypertension,^150,151 and asthma.¹⁵² Due to the wide variety of yoga practices and styles, further research is required to determine the most appropriate practices for different clinical conditions. Typical yoga sessions of different styles appear to differ in exercise stimulus, resulting in varied increase in oxygen consumption^{125,126,131,137} with profound increases reported during dynamic posture sequences compared to static posture sequences.^126,131 Different yoga practices and styles, however, are likely to have different health and fitness benefits.^153,154

It appears that breath rate and retention periods are critical in determining oxygen consumption and that yoga practitioners are able to vary their breath rate widely with reported breath rates ranging from 1 breath/min to more than 230 breath/min. Oxygen consumption is also reported to paradoxically increase by up to 10% despite breath rates of only 1 breath/min. The most profound changes in oxygen consumption with breathing techniques are seen in advanced yoga practitioners who are reported to increase their oxygen consumption by 208% and their carbon dioxide exhalation by 395% when performing Bhastrika breathing at 232 breath/min, or decrease their oxygen consumption by 16% when performing the same type of breathing at 12 breath/min. Similarly, altering the retention period during Ujjayi breathing is reported to either increase oxygen consumption by up to 52% when performed with a short retention period with an inspiration–retention–expiration ratio of 1:1:1 or decrease by 19% when the same type of breathing is performed with a longer retention period of inspiration–retention–expiration ratio of 1:4:4. Ultradian rhythms in nasal cycles and unilateral nostril breathing practices may also influence oxygen consumption with alternate nostril breathing being reported to increase oxygen consumption by up to 150%.⁹⁴

Advanced yoga practitioners appear to be able to exert extraordinary conscious manipulation of their metabolic and autonomic functions,^155,156 with reports of yogis being able to tolerate ambient carbon dioxide levels of more than 7% and oxygen levels less than 12%.⁹⁸ There are further reports of advanced yogis being able to reduce oxygen consumption by 40% while meditating in an airtight pit⁹⁹ and survive 8 days in an airtight pit with an unrecordable electrocardiogram.¹⁵⁷ These reports appear inexplicable, yet are similar to reports of advanced Zen meditators being able to decrease oxygen consumption up to 20% and dramatically reduce their respiratory rate to 1.5 to 2 breath/min during Zazen meditation, Tum-mo meditators being able to increase or decrease their oxygen consumption by more than 60% during seated meditation,¹⁵⁸ and reports of modern free divers being able to hold their breath for more than 10 minutes while diving to depths of more than 200 m.¹⁵⁹ So far, these extreme feats of metabolic control are poorly documented and limited to single case studies or small cohorts. They therefore require further investigation and documentation as they may provide clues about extending the limits of human endurance and metabolic control.

This review suggests that yoga can have profound metabolic effects with a consistent picture emerging from experimental, cohort, nonrandomized, and randomized controlled trial studies. Yet most of the studies are of poor methodological quality and do not provide adequate reporting of the study design, study population, yoga practices, methods of measurements, or statistical methods. Furthermore, most studies were performed in India (n = 35) and included only small numbers of adult male yoga practitioners without matched comparison groups. Furthermore, there are 2 randomized controlled trails of healthy people that report no change in oxygen consumption with yoga despite significant changes in other physiological measures. Of these, a controlled trial (n = 10) reported significant improvements in flexibility with yoga but no change in maximal aerobic capacity,¹²⁹ while another controlled trail (n = 18) reported improvements in respiratory variables and breath hold time but no change in oxygen consumption during submaximal exercise with yoga.¹¹³ A further cohort study (n = 10) reported significant improvements in biochemical and anthropometric parameters after 3 months of yoga practice but did not find any change in oxygen consumption.¹⁰⁹

The small sample sizes, variable practices, and limited, nonclinical populations involved in the reviewed studies make it difficult to generalize results to wider populations or make definitive statements about specific practices. Thus, more rigorous studies with larger samples and standardized practices are required to determine the role of yoga in modulating oxygen consumption and determine if the reported results can be reproduced in non-Indian, female, adolescent, and non-yoga-practicing populations as well as in different clinical conditions. The reports of advanced yogis performing extraordinary feats also warrant further investigation using modern equipment and research methodologies.

Conclusion

Research to date on yoga and metabolism includes many heterogeneous yoga practices in studies of poor methodological quality. This research suggests that yoga practices can produce dramatic changes in oxygen consumption and metabolism and that regular yoga practice may lead to reduced resting metabolic rate. Research further suggests that different yoga postures and breathing practices, which involve the control of respiratory rate and retention periods, may produce markedly different metabolic effects with reductions in oxygen consumption being more dramatic than increases. The volitional control over autonomic functions and increased metabolic endurance demonstrated by advanced yoga practitioners warrant further investigation. Rigorous research on standardized practice is required to determine the relevance of yoga practices in various clinical conditions.

Footnotes

Authors’ Note

This article was prepared as part of Anupama Tyagi’s PhD research.

Acknowledgement

The work for this article was performed at RMIT University. The authors would like to acknowledge the assistance of RMIT University biomedical librarian Savita Hazari for her help in conducting the searches and sourcing and obtaining articles.

Author Contributions

Anupama Tyagi was responsible for conducting the literature searches, preparing the tables, and writing the first draft of the article. Marc Cohen was responsible for conceiving the article, categorizing the papers, and assisting in writing the article and reviewing drafts.

Declaration of Conflicting Interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Ethical Approval

As this article represents a systematic review of literature and no human or animal experimentation, no ethics review was sought or required.

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Oxygen Consumption Changes With Yoga Practices

Abstract

Keywords

Introduction

Oxygen Consumption, Stress, and Pathology

Yoga, Stress, and Metabolism

Methodology

Results

Pranayama Practices and Oxygen Consumption

Yoga Meditation, Relaxation Practices, and Oxygen Consumption

Asana/Integrated Yoga Practices and Oxygen consumption

Regular Yoga Practice, Physical Activity, and Oxygen Consumption

Discussion

Conclusion

Footnotes

Authors’ Note

Acknowledgement

Author Contributions

Declaration of Conflicting Interests

Funding

Ethical Approval

References